Under the strategic goal of “carbon peak, carbon neutral”, CCUS technology has become an important means of reducing CO2 emissions and sustainable energy development in China. The replacement of CH4/CO2 hydrate has the advantages of being environmentally friendly and maintaining the stability of geological reservoirs. At present, the laboratory has done quite a lot of experiments and simulations on the research of natural gas replacement and recovery, but it mainly focuses on the research in coarse sand such as glass sand, however, there is little research on the real marine environment. Some studies show that porous media has a great impact on the replacement effect. This study simulates the geological conditions of the South China Sea with real natural marine sediments of the South China Sea as porous media, systematically studies various factors affecting the replacement process, and explains the change of the replacement rate and CO2 storage rate through the analysis of the driving force of the replacement process. Under different pressure (1.9-5.6MPa), temperatures (-1.82-3.87℃), and hydrate saturation (10% – 20%), the CO2/N2 mixture is used to replace natural gas hydrate in argillaceous silt. The results show that higher displacement temperature and lower displacement pressure have a positive effect on the recovery of CH4, and lower displacement pressure and higher hydrate saturation are conducive to improving the storage capacity of CO2. In marine soil sediments with low permeability, the pore size of the hydrate reservoir is small, and the contact area between N2/CO2 and methane hydrate is small, which leads to the inconspicuous replacement effect and low efficiency. According to the experimental results, we should optimize the pressure and temperature conditions, further enhance the heat and mass transfer effect, improve the permeability of the reservoir, and then improve the storage rate and replacement efficiency.
Keywords CO2 sequestration, CH4 recovery, Natural gas hydrate, CH4/CO2 replacement